Recuperator structures



y 4, 1960 F. D. HAZEN 2,937,855

RECUPERATOR STRUCTURES Filed Sept. 11, 1958 ANGLE Fig.5.

INVENTOR. Frank D. Hozen ATTORNEY Wag AW,

2,937,855 Patented" M y 9 RECUPERATOR STRUCTURES Frank 1). Hazen, 1 .0.Box 10597, Pittsburgh 35, Pa. Filed Sept. 11, 1958, Ser. No. 760,522

2 Claims. 01. 257-238) This invention relates to new and usefulimprovements in recuperator structures, more particularly to the shapingand spacing of the ends of the heat exchange tubes of metallicrecuperators. The present invention is a continuation-in-part ofapplication Serial No. 444,514 filed July 20, 1954, now abandoned.

In the former application there is disclosed metallic tube structuresmade of stainless steel in which the ends of the tubes are shaped toeliminate dead spots at the center thereof. Also the tubes are designedto prevent the collection of dust or flakes of scale in the dead airspace at the ends of the tubes by eliminating such space and utilizingthe full sweeping action of the air velocity passing through said tubes.

The present application deals with the spacing of the walls of an innerand outer tube and the shaping and spacing of the ends of the tubes insuch proportion that the cold air passing from the inner tube at the endinto the end of the outer tube and up along the space between said tubesmaintains the tube ends below the melting temperature of the metal andhas a uniform velocity flow whereby there is no interruption of the airstream that would cause stagnation or that would effect clogging byprecipitation of any particles entrained in said air.

The invention and its objects will appear more clearly from adescription of the accompanying drawing which constitutes a part hereofin which like reference characters designate like parts and in which:

Figure 1 is a view in perspective of a recuperator structure with banksof metal tubes embodying the principles of this invention.

Figure 2, a cross-sectional view of the lower end of the assembled innerand outer tubes;

Figure 3', a cross-section of the lower end of a modified form of innerand outer recuperature tube shapes.

Figure 4, a table giving the relative spacing of the inner and outertubes and the dimensions of the flow passages from the inner tube andbetween the tubes; and

Figure 5, a diagrammatic illustration of the radiation angle of the tubeshown in Figure 2.

In the drawing the numerals 1 and 2 designate the side walls of arecuperator chamber, 3 the floor thereof and 4 the ceiling. Supported onthe walls 1 and 2, which are suitably reinforced by buckstays and otherstructural steel members, are a plurality of headers 5 and 6, each ofwhich supports banks of metallic tubes 7 that are made of stainlesssteel, there being the outer tubes 7 and inner tubes 8 separated byspacers 9 as shown in Figure 2, the outer tubes being in opencommunication with a chamber 10 and the inner tubes extending upward toa chamber 11. The chamber 11 is connected to manifold 12 from which coldair is blown into the chamber and downwardly through the tubes 8 and thechamber 10 is connected by ducts 13 to a manifold 14 which collects thepreheated air passing upward from the outer tubes into chamber 10 anddelivers the same to the burners (not shown) of an industrial heatingfurnace such as a continuous billet heating furnace, also not shown. V 1

The construction of the recuperator and the manner of mounting the tubesis not novel and is no part of the present invention. It has beendescribed for illustrative purposes only.v The invention deals with theshape and spacing of the inner and outer tube ends, as shown in Figures2 to 5 of the drawings.

In the form of tube ends shown in Figure 2, the inner tube'end 15 is ofinverted frusto-conical shape open at the end, the opening beingdesignated by the reference character B. The outer tube end 16 is ofconcavo convex shape having a reentrant bottom 17. Bothvthe inner tubeend 15 and outer tubeend 16 may be cast of stainless steel or they maybe pressed to shape and welded to the cylindrical end of the tubes onthe lines 18 and 19 which are the joints; I a

In Figure 3, the end 20 of inner tube 8 is of inverted frusto conicalshape the same as in Figure 2, but the nose or end 21 of outer tube 7 iscup or dish shaped, as shown. The embodiment of Figure 3 also serves touniformly deflect the flow of air in substantially the same manner asillustrated in the embodiment of Figure 2 when the spacing of thevcylinder .walls and tube ends is carried out as hereinafter stated. Theends may be cast or pressed and welded at the joints 22 and 23.

In addition to the shaping of the ends of the tubes, as shown, toeliminate dead or heat spots, an important feature is the spacing andsizing of the air flow passages from the inner tube and-between thetubes to keep the metal temperature below melting or burning.

In Figures 2 and 3 the space between the inner and outer tube isdesignated A, the end opening of the inner tube B and the distance ofthe end of the inner tube from the end of the outer tube by thereference character C.

The spacing of the cylindrical walls of the tubes and the ends of thetubes is given in the table shown in Figure 4 of the drawing. If thespace A between the tubes 7 and 8 is inch, the distance C is 1% inchesto provide the same volume and velocity flow at all points from theopening B down to the inner wall of the ends 16 and 17 of the outer tubeand up the space A. These figures are derived from calculations todetermine the flow areas of the space between the end of the inner tubeand the end of the outer tube to be the same as the area of the annularspace A between the tubes. As shown in the table of Figure 4, thedimensions of B and C vary with A.

I have found that by so proportioning the spacing of A and C and thedimension of B, the cold air flowing from the inner tube 8 will strikethe center of the nose of the outer tube and wipe the inner wall as itpasses upward through space A between the tubes.

The cold air entering the header chamber 11 is of course somewhatpreheated by the warm air flow upward around the space A to the outletheader chamber 10. However, by maintaining the velocity and volume ofthe air flow constant in accordance with the proportioning of the flowpassages, as shown in the table of Figure 4, dead 7 Although severalembodiments of the invention have been herein illustrated and described,it will be evident to those skilled in the art that variousmodifications may be made in the details of construction withoutdeparting from the principles herein set forth. Notice is given of myapplication Serial Number 293,091 filed June 12, 1952 now abandoned, ofwhich earlier application the application for these Letters Patentcomprises a continuationin-part.

I claim:

1. A metal recuperator for industrial heating furnaces including a heatexchange structure comprising banks of tubular heat exchange memberssuspended in a hot gas flow passage, said members consisting of outertubes and inner tubes spaced from each other to provide an air fiowpassage therebetween, said inner tubes being open at both ends and saidouter tubes each having a closure at one end constituting a centraldeformed deflecting portion deformed in the direction of the outlets ofthe inner tubes having a curved surface for directing the flow of coldair from the open end of the inner tubes to the air flow passagebetweensaid tubes in wiping contact with the curved surface of theclosure end of the outer tubes, and the end ofthe inner tubes adjacentthe closure of the outer tubes being of inverted frusto-conical shape todirect the air flow to strike the center of the curved surface of theclosure, the open end of the inner tubes being spaced from said curvedsurface a distance in such proportion to the diameter of the inner tubeopenings that the flow area corresponds to the flow area of the annularspace between the inner and outer tube walls so that the cold air passesfrom the open ends of the inner tubes against the curved surfaces of theclosure and along the air flow passage between said tubes at uniformvelocity and volume to maintain said tube ends and outer tube wallsbelow the melting temperature of the metal of which the tubes are made.

2. A metal recuperator for industrial heating furnaces .4 including aheat exchange structure comprising banks of tubularheat exchange memberssuspended in a hot gas flow passage, said members consisting of outertubes and inner tubes spaced from each other to provide an air flowpassage therebetween, said inner tubes being open at both ends and saidouter tubes having a reentrant closure at one end of concave-convexshape to provide curved air flow surfaces for directing the flow of coldair from the inner tubes to the air flow passage between said tubes inwiping contact with said curved air flow surfaces, the open end of theinner tubes being spaced from said curved air flow surfaces a distancein such proportion to the diameter of the inner tube openings that theflow area cor responds to the fiow area of the annular space between theinner and outer tube walls so that the cold air passes from the openends of the inner tubes against the curved surfaces of the closure andalong the air flow passage between said tubes at uniform velocity andvolume to maintain said tube ends and outer tube walls below the meltingtemperature of the metal of which the tubes are made.

References Cited in the file of this patent UNITED STATES PATENTS

